1. Field of the Invention
The invention concerns a fluid flow calorimeter and more particularly, but not exclusively, a flow calorimeter intended to measure the enthalpic differences of fluids at low temperature and at high pressure.
2. Description of the Prior Art
It is known that the constant fluid flow-rate method can produce very good results while offering a practical utilization. This method consists in causing to pass the fluid, at a predetermined temperature, with a fixed mass-flow-rate and maintaining a constant pressure, in a calorimeter where the electric power is transmitted thereto and where the temperature rise undergone by the moving fluid is measured.
The enthalpy variation corresponding to this temperature rise is equal to the electric power/fluid flow-rate ratio.
Several attempts have been made to reduce to practice this measuring principle, at low temperature and at high pressure, and among the various apparatus proposed can be cited a number of calorimeters in which the temperatures measured are the skin temperatures of the walls of the apparatus in order to prevent all possible leaks. T. MIYASAKI in "J. Chemical Thermodinamics 1980" (A New High Pressure Recycle Flow Calorimeter) proposes bringing the wires of heating resistance and the wires for simultaneously measuring the temperatures through the intermediary of a sheath, up to ambient temperature.
These devices present major drawbacks. On the one hand, they are often very space-consuming and require high flow-rates. Furthermore, they do not offer very accurate results, either because the temperatures measured are not the temperatures of the fluid itself (skin-temperature) or because the conduction due to the input sheath of the wires does not permit a real measurement of the temperature. Similarly, in certain cases, the proximity of the measuring wires and the power wires provokes an increase in temperature of the measuring wires that impairs the accuracy of the measurement.